1. Field of the Invention
The present invention relates to a semiconductor device capable of protecting an internal circuit from an ESD impact, damage and a mistaken working caused by an electrostatic discharge, a surge pulse and a noise, and more particularly to a semiconductor device capable of protecting an internal circuit from an external abnormal input without a protection circuit.
2. Description of Related Art
Shown in FIG. 1 is a conventional electrostatic discharge protection circuit (hereinafter, referred to as an ESD protection circuit). Referring to FIG. 1, an external signal input through an input pad 10 is input into an internal circuit 40 through a pre-buffer 30 after passing through the ESD protection circuit 20. The internal circuit 40 are provided with power from a power supply Vdd, and provided with a second power from a ground voltage level GND.
The ESD protection circuit 20 includes a PMOS transistor 21 and an NMOS transistor 22, each of which acts as a diode. The gate and drain of the PMOS transistor 21 and a well where it is formed are coupled to the power supply Vdd, and also the source thereof is coupled to a node N1 in a conduction line 70 which is couple to the input pad 10 and the power supply Vdd. This PMOS transistor 21 acts as a diode between node N1 and the power supply Vdd. The gate and drain of the NMOS transistor 22 and a well where it is formed are coupled to a ground voltage level GND, and also the source thereof is coupled to a node N1. Accordingly, the NMOS transistor 22 acts as a diode between node N1 and the ground voltage level GND.
In other words, the ESD protection circuit 20 inputs an input signal only between -0.7 V and 5.7 V (in case of operation voltage of 5 V) to the pre-buffer 30 and protects the internal circuit 40 by discharging other voltage levels to the power supply Vdd and the ground voltage level GND.
As a result, since the conventional ESD protection circuit uses transistors for discharging the ESD impact in a chip, the occupying area of the ESD protection circuit considerably increases as comparing that of the internal circuit with the development of the integrated circuit. In addition, the protection of the internal circuit is limited in the difficulties in processing steps to improve the electrical characteristics of the ESD protection circuit.
Further, to solve signal noise generated when the semiconductor chip is mounted on the PCB, the conventional ESD protection circuit has additionally used a zener diode and a diode array filter relay circuit. However, this method requires the high cost of production and there is still a problem in that the semiconductor chip leads an error into its operation.